Manufacture of purified zinc



Sept. 22, 1936. L s. DEITZ., JR.. ET AL 2,055,195

MANUFACTURE oF PURIFIED ZINC Filed May l, 1935 2 Sheets-Sheel' `l L. s.o/Erz JR. a. ,u /vsr/ELD /NVENTORS Sept. 22, 1936.' 5 DElTZ, JR, ET AL2,055,195

MANUFACTURE OF PURIFIED ZINC Filed May l, 1935 2 Sheets-Sheet 2 ATTO EYvfil() .in the manufacture of ne chemicals.

Patented Sept. 22, ,i936

autant rica WANUFACTURE F P Application May li, 11935, Serial No.3.9,140

(Cl. l-d8) 2@ Claim.

This invention relatesnto the manufacture of puriiiedzinc, and moreparticularly to methods of making zinc dust and spelter.

Zinc spelter and zinc dust have been produced heretofore from impurematerials containing zinc, such as die castings, zinc drosses from diecasting and galvanizing processes, and other forms of scrap zinc.Zinc-bearing materials of this nature contain many undesirableimpurities, most ci which are removed or materially diminished in themanufacture of the nished product. Some forms oi raw or virginlzinc alsocontain unwanted impurities. The usual process of making zinc spelterand zinc dust is to distil the zinc from a charge of impure material ata temperature at which the zinc will vaporize, but at winch largequantities of the undesired ingredients in 'the charge will notvaporize, and then to condense the resulting zinc vapor in a condenserdesignedto cause the zinc to collect in the form oi a liquid or solidbody, or as dust,- 'depending upon which product is desired. In theprocesses formerly used the bulk of the impurities in the scrap mno wereretained in the distilling retort, but some impurities, particularlylead, tended to distii over with the zinc and contaminated the iinishedproduct. For some purposes, zinc containing a small amount of leadissatisiactory, but many processes require the use of zincwhich is asfree from lead as possible. An example of this is the use of zinc dustas a reducing agent The presence oi lead in zinc dust used for thispurpose is very undesirable and zinc dust made in the usual way fromzinc scraps containing appreciable quantities of lead is not suitable.

The objects of the' invention are tol provide metallic zinc and zincdust of a desired purity and great uniformity, and to supply economical,

simple and effective vmethods of producing metallic zincand zinc dusthaving these characteristics. l

` These objects are attained in accordance with the invention bydistilling zinc from impure materials containing zincin the presence o1'a metal,

such as iron, which inhibits or retards the distillation oi lead, andcondensing the resulting zinc vapor in a suitable condenser.

`The above described and other objects and features of the inventionwill be apparent from the following detailed description" taken inconnection with the annexed drawings, in which- Fig. l is a side view,partlyl in section, of an apparatus designed to produce zinc dust,

Fig. 2 is a temperature-time chart showing the temperatures which obtainat apredetermined point within a portion of the apparatus shown in Fig.l during the operation thereof, and

Fig. 3 is a verticalV sectional View of an apparatus designed totproduceainc spelter.

In practicing the invention, a charge ill of impure zinc, such as scrapzincor impure raw zinc, and suiiicient iron to retard or inhibit thedistillation of the lead in the impure zinc is added to a retort ii. Inthe preferred embodiment of the invention the quantity of iron presentin the charge is about three to four parts for each part of lead in thescrap zinc, a ratio of 3.5 parts of iron to 1 part of lead having provedto be a suitable one. The iron employed may be in any desired form, butordinary scrap iron is a satisfactory material'to add to the charge toadjust 'the iron content to the desired value.

The retort il, which is made oi graphite or other suitable refractorymaterial, is supported in avfurnace designated generally by the numeralH3, which is heated by an oil burner or by any other suitable means. bemade is zinc dust, a condenser orv dust box i5 is rolled on wheels lS--ior otherwise advanced into a position adjacent the retort il 1f the nnalproduct to so that a connector il carried by the condenser or dust .boxi5 coincides with the opening in theneck of the retort il. An airtightjoint is effected between the connector il and the open end of theretort il by means of a. luting i9 of clay or other suitable material, asimilar joint having been made previously between the connector l'l andthe condenser l5 by means of a luting 20. The condenser l5 is providedwith thin walls made of a strong, heat-'conducting material, such assheet iron, and is provided with a door 22 for the removal of zinc. dustfrom. the interior of the condenser.

When the charge of impure zinc and iron has been introduced into theretort li and the neck i1 has been sealed to the retort ll by the lutingi9, the temperature of the furnace i3 is raised to a point where thezinc distils from the charge but the impurities containedth'erein do notdistily vwith the zinc. The resulting zinc vapor passes within thecondenser is maintained at a point' tion thereof into zinc dust iscontinued until the zinc in the retort I I is almost exhausted, when thefurnace is shut off, and the retort is disconnected from the condenserand allowed to cool. In orzinc, the furnace is regulated to slow up thedistillation and, conversely, when the temperature within the condenserfalls too low the distillation Vis speeded up in order that the processmay be carried out as rapidly andefciently as possible.

In order to determine the temperature of the zinc vapor within thecondenser, a thermocouple (not shown) .is inserted in` the top of thecondenser I5 at' about the center thereof and isconnected with anautomatic temperature recording device (not shown), wherebyl thetemperature Within the portion of the condenser adjacent thethermocouple is continuously recorded. Suitable types of thermocouplesand temperature-recording devices are well-known and. since theparticular construction of these devices forms no part of theinvention,v it is not necessary to.. describe them in detail.

It has been found that if the charge in the retort isvheated until all`of the zinc in the charge is distilled, the bulk of the lead in thecharge is held therein by the iron during practically all of thedistillation period, but that a substantial quantity of lead distilsover with the last portions of the zinc. Although it is diiiicult todetermine definitely what causes the iron in the charge to inhibit thedistillation of lead, it is believed that a zinc-lead-iron alloy islformed in the charge which reduces the vapor pressure of thelead. As aresult, the zinc distils over for a considerable period with a leadcontent materially less than would be the caseif the iron were omittedfrom the charge and this condition will prevail until the supply of freezinc in the charge becomes almost exhausted. When the amount of freezinc becomes depleted, th'e vapor pressure of the zinc decreases, thevapor pressure of the lead increases and some lead is distilled with thezinc. Probably the lead is held in the zinc-leadiron alloy until thefree zinc Areaches a. certain value when the alloy is decomposed andreleases the-lead. Whatever the correct explanation of the phenomenonmay be, the process provides a practical way of retarding thedistillation of lead from impure zinc containinglead and the inventionis not to be limited by the theory outlined herein. l A Inorder to avoidthe `distillation of an undesired quantity of lead with the zinc, thedistillation is stopped before the zinc in the charge is completelyexhausted. It has been observed that the temperature of the zinc vaporin the condenser suddenly falls at about the time the transformationfrom the distillation of substantially pure zinc to the distillation ofsubstantial fquantities of lead along with the zinc occurs. This rapidfall in temperature is probably caused by a decrease in. the quantity ofzinc vapors that reaches the condenser and provides a convenient meansof determining when to en d the distillation of the charge. y

After the apparatus has been in operation long enough to learn itscharacteristics, the approximate time required to distil the zinc from agiven charge in the retort II may be readily estimated and when thedistillation period is about over the temperature chart of the recordingthermometer is observed inorder that the distillation operation may bestopped at the desired point. The end point of the distillation isdetermined by noting on the record of the temperature within. thecondenser the point at which the temperature begins to fall rapidlyueven though the furnace is operating at a normal temperature. When thetemperature suddenly falls, distillation is stopped by shutting off thefurnace and disconnecting the condenser from the retort. After theretort has cooled sufficiently the residue of the charge is removed fromthe retort, a fresh charge of impure zincl and iron is introducedtherein, the condenser is again connected tothe retort and the abovedescribed operations are repeated.

Although the size and relative proportions of the parts of the apparatusused to practice the invention may be varied, it has been found thatsatisfactory results may be obtained by employing a retort holding acharge of about 3500 pounds of impure zinc and by providing a furnace-and condenser of the requisite sizes and proportions to permit thedistillation and condensation of this charge in about eighteen hours.'Assumng that the charge of 3500 pounds of impure zinc contains from 1.25to 1.5% of lead, a-

suiicient quantity of iron, such as scrap iron, is included in thecharge to provide about 3.5 parts of iron for each part of lead in thecharge. That is, if theL charge of, scrap zinc is free of iron, fromabout to. 185 pounds of scrap iron are added to the charge. If thecharge of scrap zinc contains iron as an impurity, the amounty of scrapiron added is reduced accordingly. Scrap zincs from different sourcesmay contain varying amounts of iron as impurities and scrap materials ofthis character may be mixed with each other and with scrap iron in suchproportions that fthe resulting mixture contains about 3 t0- 4 parts ofiron per part of lead therein.

It has also been found that a very satisfactory zinc dust which is ofgreat fineness and uniformthe automatic temperature recorder of the tem-This chart represents the record made during a complete cycle of theprocess by till perature within the upper portion of the condenser asdetermined by the thermocouple positioned therein. The numbers aroundthe circumference ofthe chart designate time in hours, while the numbersalong the substantially radial lines indicate temperature .in degreescentigrade. The record illustrated was started at the point X and endedat the point Y with the recording pen moving relative to the chart inthe direction indicated by the arrow. Along the portion A-B of thetemperature curve on this chart, the con denser has just beendisconnected from thevretort after one charge has been distilled and,consequently, the temperature within the condenser is falling. Thisrepresents that period in the cycle during which the retort is coolingoil, is belng cleaned and is being refilled with a fresh charge ofimpure zinc and iron.

At about the point B the condenser is connected to the retort and thefurnace started up again; and at about the point C distillation lne--gins. The temperature within the lcondenser then immediately begins torise and continue to rise until it reaches a value indicated by letterD, that is in the vicinity of350 C. The furnace` is so regulated thatthe temperature of the zinc vapor within the condenser which is adjacentthe thermocouple is maintained at approximately 350 C. and thiscondition prevails until the point indicated by the letter E on thetemperature curve is reached. .dt this point the temperature curve takesa very decided drop, although the furnace is still .operated at itsnormal temperature, and when this occurs the distillation is stopped byshunting ofi the furnace and disconnecting the condenser from .theretort.

It will be observed that the entire cycle takes approximatelytwenty-four hours and that the portion of the cycle during winchdistillation takes piace requires about eighteen hours. When almosteighteen hours of the distillation period have elapsed, the operator ofthe apparatus watches the temperature record made by the recordingapparatus on the chart in order that he may note when the temperaturecurve shows ya definite dropping on, although the furnace isstilloperating normally, whereupon he immediately stops the process.

By 'practicing the method just described, the bull; of the lead isretained in the residue left in the retort and the zinc dust issubstantially free ci lead. The zinc dust produced by this methodusually contalns'less ythan .1% of lea/d, and almost never contains morethan .15% lead. Ob

viously, when retorts and'condensers of dinerent sizes are employed, thevarious phases of the cycle will require different periods of time forcompletion. Nevertheless, the process is prefer-l ably practiced in suchmanner that the distillation operation is stopped before substantialquantities of lead are distilled.

When it is desiredto produce zinc spelter in.- stead oi zinc dust, thecondenser lb is replaced by a smaller condenser designed to condense thezinc vapor in the form of a liquid or a solid instead of in very fineparticles. v ACcndensers suitable for this purpose are well-known in theart and many types of condensers are used for producing spelter. Onetype of condenser which is satisfactory is illustrated in Fig. 3 ot thedrawings, in which M3 indicates generally an oil-nred furnace in which aretort Iii is positioned. A condenser H5 is held in position adjacentthe retort iii by anysuitable means, such as chains I iS-l It, connectedto any suitable support, such as a chain hoist (not shown). Thecondenser lib is connected to the retort iii by means of a connector liland an airtight Joint is eiected between the connector ill, the retortMi and the condenser H5 by means of ltings llt and 82d of clay or othersuitable material. The condenser il E comprises a cylindrical ironcasing itl which is 4closed at one end by a plate itt and whichis in theform of a truncated cone i3d at the opposite end to provide a neckportion for the entrance of zinc vapor. 'I'he retort is lined with arefractory lining t28 made of a suitable heat insulating material, suchas tile made in suitable shapes, which retards the flow of heat from thezinc va-` por entering the retort to the exterior thereof. The condenseris provided with an opening it@ to permit the exit of gases from thecondenser, if desired, and with a tap hole iti through which liquidzinc, which collects in the condenser, may be tapped on when desired.The tap hole ist is normally closed `by a plug of any refractorymaterial, such as clay,'and the opening itt may also be plugged up in asimilar manner if desired.

When it is desired to vgain access to the Ainterior of the condenser toclean it or repair the lining,

`lthe end plate ill may be removed bydisconnecting bolts itt-33.likewise, the truncated end portion it may be removed by disconnectingbolts i3d-43d.`

ln the operation of this apparatus, the retort zinc and about three tofour parts of iron per part of lead in the charge, and the retort isheated to cause the distillation oftheV aine from the charge. Y The zincvapor which is produced passes through the connector lil into thecondenser lib where it is cooled sumciently to convert it into theliquid state. The condensed liquid aine which collects in the bottom ofthe condenser lib is tapped oli at intervals through the tap hole itiinto a, ladle and is cast into slabs.

Since the zinc collectedfin the condenser lib is cremoved. from time totime, it is possible to continue the process until all of the eine inthe charge is distilled, if desired. In this case the zinc collected inthe last fraction of the distillate would not be mingled with thatcollected in previous Afractions because` the last fraction wouldcontain a substantial quantity of lead. 0r, the process can be stopped,as is done in the manu facture of zinc dust, at the point where the leadbegins to distii over in appreciable quantities. By either process zincspelter which is substan tially free of lead is produced.

ile specific types of apparatus by means of which the invention may bepracticed have been described, it is ofcourse tobe understood that theprocess may be performed in different kinds of apparatus. Furthermore,the process may be varied in a number of particulars without departingfrom the invention. For example, the

- iii is partly lled witha charge il@ of impure charges which areintroduced into the retorteA it and iid need not necessarily be chargesor solid material, but the impure zinc maybe in-=1 troduced into theretorts either intermittently or continuously in the liquid state. ereit is not essential that the zinc produced be substan tially free from.lead. but' it is desired to have the lead content'therein at a lowvalue, the

amount of iron in the charge may be proportiondistilled at a more rapidrate than would be permissible ifno metal were added to the charge whichinhibits the distillation of the lead. 'Ihe invention thus permits theproduction of a better quality and more uniform zinc than that hithertoproduced from similar materials and at the same time permits a greateroutput of zinc over a given period of time than Was/heretoforeobtainable from the same equipment.

Whatis claimed is:

1. The method of producing zinc, which comprises distilling zinc from acharge containing zinc contaminated with lead and suilicient iron tosubstantially, completely inhibit the distillation of any of the lead inthe charge, and condensing theresulting zinc vapor.` 2. The method oi.'producing zinc dust, which comprises distilling a charge containing zinccontaminated with lead and suiilcient iron to substantially compieteiyinhibit the distiliatin of any of the lead in the charge, and condensingthe resulting zinc vapor under such conditions thatthe zinc solidies inthe form of dust.

3. The methodof producing zinc spelter, which comprises distilling acharge containing zinc contaminated with lead and suiiicient iron tosubstantially completely inhibit the distillation of any of the lead inthe charge, and condensing the resulting zinc vapor under suchconditions that it collects in a liquid body. i

4. Thegprocess of producing zinc having a low lead content, whichcomprises distilling zinc from zinc-bearing material in the presence ofsufiicient iron to substantially completely inhibit the distillation ofany oi the lead, 'condensing the resulting l zinc vapors, continuingthedistillation until the proportionA of lead which distilswith the zincreaches a predetermined value, and then stopping the process. .v 5. Theprocess of making zinc dust, whichcomprises dlstilling zinc fromzinc-bearing material in the presence of suilcient iron to substantiallycompletely inhibit the distillation of any of the Jead, condensingtheresulting zinc vapor under. conditions suitable to` produce` zincdust,- and stopping the process prior to the point where lead begins toaDpear'in the zinc dust in undesired quantities.

- 6. The process o! producing puriiled zinc from zinc-bearing materialcontaining leali,l which comprises distillinga charge containing saidmaterial and sumcientiron to provide about 3 to`4 parts of iron per partof lead in Ysaid material, and condensing th resulting zinc vapor. 7.The process o? making zinc dust ffrom zinc'- bearing material containinglead, which comprises distilling a: charge containing said material andsuilicient iron to provide about 3 to 4 parts oi.' iron lper part oilead in said material, and condensing the resulting zinc vapor undersuch condition that the zinc solldifies in the form of dust. 8. Theprocess of making zinc spelter from zinc-bearing material containingvlead, which comprises distilling a charge containing said material andsuiiicient iron to provide about 3 to 4 parts ot iron per part oi' leadin said material,`

and condensing the resulting zinc vapor under such conditions that itcollects in a liquid body. 9. The process oi producing purified zincfrom zinc-bearing materials containing lead, which comprises charging aretort with a charge consisting of such zinc-bearing material andiron lin the ratio of about 3 to 4 parts of iron to each part of leadcontained therein, distilling said charge, condensing the resulting zincvapor, and stopping lthe process prior to the point where thelead'begins to distilv with the zinc in undesired quantities. A

10. The process of making zinc dust from zincbearing materialscontaining lead, which comprises charging a retort with a chargeconsisting of such zinc-bearing'material and iron in the ratio of about3 to 4 parts of iron to each part of lead contained therein,distillinglsaid charge, condensing the resulting zinc vapor under suchconditions that the zinc solidies in the form of dust, and stopping theprocess prior to the point 4where the lead begins to distil with thezinc in undesired quantities.

11. The process of making zinc spelter from zinc-bearing materialscontaining lead, which comprises charging a retort with a chargeconsisting ofsaid vzinc-bearing material and iron in the ratio of about3 to 4 parts of iron to each. part of lead contained therein, distillingsaid charge, condensingthe resulting zinc vapor under such conditions'that the zinc collects in a liqiiid body, and stopping the processprior to the pointA where the lead begins to distil with the zinc inundesired quantities.

12. 'I'he method of producing zinc, which comprises distllling zinc froma charge containing zinc contaminated with lead and sufdcient iron tosubstantially completely inhibit the distillation of any of the lead,condensing the resulting "vapor, and stopping the process before all ofthe zinc has been distilled from the charge but after the maior portionof the zinc has been distilled therefrom, whereby the zinc produced issubstantially free of lead.

13. 'I'he method of producing zinc, which com` prises preparing a chargecontaining iron and zinc contaminated with lead in which the amount ofiron bears a denite relationship to the amount of lead thereindetermined by the degree of freedom from lead desired in the riishedproduct, heating the charge to distil zinc therefrom,and condensing theresulting zinc vapor. A

14. The method of producing zinc from leadbearing zinc scraps containingiron in varying scraps with each other and with substantiallyproportions, which comprises mixing the zinc pure iron in suchproportions that the resulting mixture contains about 3 to 4 parts ofiron per partsof lead therein, heating the mixture to distil zinctherefrom, and condensing the resulting zinc vapor. A

15. The method of producing zinc from impure zinc containing lead, whichcomprises mixing the impure zinc with suilicient scrap iron to provideabout 3.5 parts of iron per part of lead I in the zinc, heating theresulting mixture to distilzinc therefrom, and condensing the resultingzinc vapor. u

16. The method of making zinc spelter, which comprises distilling zinclfrom a charge containing zinc contaminated with lead and suilcient ironto substantially completely inhibit the distillation of any of the lead,collecting the major portion of the condensed zinc in one body, and

` collecting thelast portion of the condensed zin( in another body,whereby the bulk of the spelter produced is substantially free of lead.

17. The process of producing zinc dust of low lead content and ofuniform quality, which comprises introducing into a retort a chargecontaining zinc. lead, and sufficient iron to substantially completelyinhibit the distillation of any of the lead, heating the retort todistil the zinc from said charge, conducting the resulting zinc vaporinto a large heat conducting condenser whereby the vapor is condensed inthe form of dust, regulating the heat applied to the retort so that thetemperature at a given point within the condenser is substantiallyuniform, continuing the aforementioned operation until the temperatureat said point falls rapidly, and then stopping the process.

18. 'I'he process of producing zinc dust of low lead content and ofuniform quality, which comprises introducing into a retort a chargecontaining zinc, lead, a'nd about 3 to 4 parts iron per part of leadtherein, heating the retort to distil the zinc from said charge,conducting the resulting zinc vapor into a large heat conductingcondenser whereby the vapor is condensed in the form of dust, regulatingthe heat applied to the retort 'so thatthe temperature at a given pointwithin the .condenser is substantially uniform, continuing theaforementioned operation until the temperature at said point fallsrapidly, and then stopping the process.

19. The method of producing puried zinc,

ywhich comprises distilling a charge containing zinc-bearing material,lead and sucient iron to substantially completely inhibit thedistillation of any of the lead in the charge.

20. The method of producing zinc, which comprises adding to a chargeofzinc-bearing material contaminated with lead a sumcient quantity ofiron to substantiaily'completely inhibit the distillation of anyof thelead in said material, and heating the' charge to distil the zinctherefrom.

- LOUIS sco'r'r nariz, Jn.-

BERNARD MANsFmin.

